Gas Membrane Gas sensors are combination electrodes that detect dissolved gases in a solution. No external reference is required for these electrodes. The sensing element is separated from the sample solution by a gas permeable membrane. Hanna’s offering of gas membrane ISEs include ammonia and carbon dioxide. Theory: A gas sensor works due to the partial pressure of the measured gas in solution. The dissolved gas in the sample diffuses into the membrane and changes the pH in a thin film of unbuffered electrolyte on the surface of the internal pH sensor. Diffusion continues until the partial pressure of the sample and the thin film of electrolyte are the same. The pH change is proportional to the dissolved gas in the sample. Reference and Combination Electrodes Hanna’s reference electrode is used with our half-cell ISE sensors to provide accurate and repeatable measurements. Hanna’s combination electrodes incorporate the measuring electrode with the reference, making them ideal for field measurements. Reference Reference electrodes are used to provide a stable voltage and electrolytic contact to measure a voltage gradient across a measurement membrane. Hanna has designed an easy to use, durable, double junction, quick-fill, sleeve-style reference electrode with a cone style junction to work with the ISE family of sensors. The design forms the liquid junction with the test solution at the tip of the junction cone, producing a highly stable reference electrode with reasonable, low flow rates. The model HI5315 is a silver/silver chloride half-cell with a permanent gel-filled internal cell. The outer fill solution is easily replaceable and serves as a buffer zone between the internal chloride ion-containing gel and the sample solution. Hanna offers a complete line of silver-free fill solutions to optimize your ion measurement. A fast responding liquid junction, excellent reproducibility, and ease of use will mark this reference as your “best” in the lab. Combination Combination electrodes include a sensor and reference electrode within one electrode body. Our combination ISEs provide the same selectivity and response as our ISE half-cells, but include our superior double junction reference in the same electrode body. Combination solid-state electrodes have a built-in solid-state sensor and quick refillable reference electrode. Our liquid membrane and fluoride combination electrodes have replaceable module construction and the Hanna double junction reference stability. 3 ISE 3.3 www.hannainst.com | introduction
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